1. Field of the Invention
The present invention relates generally to ultrasonic test head equipment and, more particularly, to equipment and methods for rapidly and reliably conducting ultrasonic testing including ultrasonic testing of multiple diameter oil field tubulars.
2. Description of the Background
The American Petroleum Institute (API) provides testing standards for oilfield tubulars. An oilfield tubular with a leak, a visually undetectable but internally corroded pocket, a hairline fracture, or other type of defect may create a hazardous condition and/or result in a costly and time consuming repair operation. Defects in oilfield tubulars have resulted in accidents causing injury, loss of expensive drilling strings, lengthy fishing jobs, and loss of recoverable hydrocarbons. Thus, it is cost effective and desirable to avoid a very expensive problem by the relatively inexpensive expedient of tubular testing.
Electromagnetic and/or ultrasonic testing of oilfield tubulars such as casing, drill pipe, and tubing is typically performed as a preventative measure after manufacture of the tubular. While electromagnetic testing of certain oilfield tubulars has been required for some time as per API standards, it is now recognized that ultrasonic testing is often a more critical test with respect to certain important factors such as wall thickness measurements and internal flaws. In fact, future API standards will require certain types of oil field tubulars to be ultrasonically tested.
Ultrasonic testing of oilfield tubulars is a relatively new service that has become available only in the last fifteen years or so. It has tended to be a rather time consuming procedure. However, if it is required by API standards that a substantial portion of the output of oilfield tubulars from the steel mills be ultrasonically tested, then large numbers of oilfield tubulars will need to be tested in a relatively short time period. Even with advances in ultrasonic test heads made in the last decade that provide more ultrasonic channels and a vastly increased helical advance per revolution of the tubular, ultrasonic testing has remained too slow to efficiently test the large numbers of oilfield tubulars that are produced by the steel mills. Thus, one of the most significant problems of prior art ultrasonic test heads is a slow testing speed.
General features of ultrasonic tubular testing equipment typically include drive means to translate/rotate a test head having one or more ultrasonic transducers with respect to the oilfield tubular to be tested. The test head and drive means typically produce a helical ultrasonic scanning pattern along the length of the oilfield tubular. For this purpose, the tubular may be held stationary while the test head moves over the exterior of the tubular. Alternatively, the ultrasonic test head may be stationary while the tubular is moved. To provide the helical scan pattern along the length of the tubular, it is necessary that the tubular rotate as well as move axially with respect to the ultrasonic transducer.
During the testing procedure, it is desirable to scan the tubulars slowly enough so as to reliably test the entire relevant surface area of the tubular. In other words, it is desirable to consistently provide a constant 100% scanning coverage of the tubular and avoid skipping over any portion of the tubular that might include a defect. On the other hand, it is also desirable to scan each tubular as rapidly as possible and without unnecessarily duplicating any testing.
While it is generally known to construct multiple ultrasonic linear arrays to increase the speed of inspection, the use of linear arrays also vastly complicates the problems of ultrasonic testing because of the large number of interrelated variables involved. Some of the factors and problems involved in utilizing ultrasonic linear arrays are discussed in the article "Ultrasonic Transducer Array Configuration for Interlaced Scanning" by K. H. Beck, Materials Evaluation, Vol. 44, May 1988, page 771-778. As stated therein, the denser interlacing arrangements used for this application with less than 180 degrees separation between the probe lines have resulted in fairly complex, inflexible, and inconvenient probe mounting and adjustments. Patents, such as U.S. Pat. Nos. 3,828,609 and 4,487,072, describe the general background and operation of ultrasonic testing equipment.
Ultrasonic linear array test heads provide an interlaced scanning configuration that is not efficient for each size diameter of pipe due to the numerous scanning factors that affect the skew angle or flaw pitch angle encountered as the surface of the tubular product passes by the test head at a fixed helix relative to the test head. Properly matching the optimal ultrasonic array configuration to the tubular diameter, the axial and rotational speeds of the tubular relative to the array, the diameter beam of each ultrasonic transducer, the orientation of the transducers, the distance from the transducers to the tubular, and the like, is difficult and time consuming.
Optimal array configuration means that the array provides a constant 100% scan of the tubular without unnecessarily duplicating the scan of all or part of the tubular. Given the numerous factors involved, prior art ultrasonic test heads employing linear transducer arrays frequently may not be efficiently adjusted to all tubular diameters and the related skew angles, and therefore sometimes scan less than 100% of the desired tubular to be tested. A defect may pass through the testing device undetected while other areas of the pipe are unnecessarily scanned multiple times.
Another related problem encountered during ultrasonic testing of tubulars is that of efficiently testing tubulars of varying diameters. U.S. Pat. No. 4,088,328 discusses a rapid changeover multi-diameter ultrasonic tube inspection system with rapid changeover features, and explains some of the difficulties involved in testing related tubulars used in nuclear power plants having varying diameters. As discussed in U.S. Pat. No. 4,088,328, the changeover time for converting some systems to handle different diameter tubulars may range from about four to eight hours. However, in the nuclear industry the need to test tubulars at high speeds is not nearly so great as it is in the oil industry.
Consequently, there remains a need to quickly and reliably provide adjustments to test heads that comprise multiple linear arrays of transducers to compensate for the varying skew angles created when tubulars are tested with different outside diameters or when increased helical advance speeds are used. Furthermore, there remains a need for an ultrasonic testing apparatus and method and that offers higher speed ultrasonic testing of oilfield tubulars that reliably provides constant 100% coverage thereof for a reasonable capitol investment. Those skilled in the art have long sought and will appreciate that the present invention provides solutions to these and other problems.